Detection and characterisation of liver metastases

Modern liver imaging of cancer patients requires an imaging modality that is not only highly sensitive in detecting lesions but also provides reliable characterisation of lesions and thus allows differentiation of metastases from frequently found benign lesions. Conventional ultrasound (US) has a relatively poor sensitivity and specificity for imaging liver metastases and US used to be inferior to CT and MRI mainly due to a lack of contrast agents. This has changed with the advent of microbubble contrast agents for US. The use of recent contrast agents such as SonoVue (Bracco, Italy) combined with low mechanical index contrast-specific imaging techniques such as Contrast Pulse Sequencing provides dynamic real time imaging of focal liver lesions in the arterial, portal venous and delayed phase. This improves lesion detection and characterisation. To investigate the benefit of SonoVue for detecting liver metastases we studied 40 cancer patients with liver lesions on reference imaging (CT or MRI), 37 of them had metastases. The mean number of reference confirmed metastases per patient increased from 1.85+/-1.79 on conventional ultrasound to 2.73+/-2.50 post SonoVue (p < 0.05). CEUS showed more individual metastases than baseline in 12 (34%) patients. Using CT or MRI as the reference, the mean sensitivity to individual metastases increased from 69% on baseline US to 90% post contrast (p < 0.0005). The role of SonoVue in characterisation of focal liver lesions was evaluated in 63 patients. One lesion was studied per patient. Based on standardised dynamic enhancement criteria for each lesion type, the number of correctly diagnosed lesions improved from 41 (65%) on baseline US to 58 (92%) post contrast (p < 0.001). On CEUS all 27 metastases were correctly diagnosed, while baseline US misinterpreted 2 of these. The number of correctly diagnosed benign lesions (n = 28) increased from 12 (43%) on baseline to 25 (89%) post SonoVue. In conclusion, detection and characterisation of focal liver lesions by US are markedly improved by the use of SonoVue. Contrast agents add a new dimension to sonography allowing it to rival CT and MRI, especially for lesion characterisation.